This invention relates to an immunoassay method in which for example, when a component in a body fluid such as serum, plasma, etc. is measured, only this objective substance can be quantitated rapidly with high precision by suppressing or avoiding the influence of a nonspecific turbidity produced by a combination of a component other than the substance to be measured in a test sample and a component in a reagent solution on the measurement.
In recent years, autoanalyzers capable of analyzing many samples for many items at the same time have spread, and attempts have been made to apply to the autoanalyzers a method for measuring a trace component in a sample derived from a living body, on the principle of so-called immunoturbidimetry (TIA) in which an objective component is measured by measuring a turbidity change caused by antigen-antibody reaction, or so-called immunonephelometry (NIA) in which an objective component is measured by measuring a scattered light intensity change caused by antigen-antibody reaction.
Such methods, however, are disadvantageous in that high-precision measurement of an analyte to be measured is hindered by a turbidity (chyle) due to a lipoprotein present in a sample or a so-called non-specific turbidity, i.e., a turbidity produced by the reaction of a component in a reagent solution with, for example, a complement (e.g. Clq), rheumatoid factor (RF) or a heat-denatured protein produced by decomplementation by heating.
For avoiding the influence of chyle on the measurement, a method comprising previous addition of a surfactant to a reagent solution is known. However, the nonspecific turbidity due to, for example, Clq, RF or the heat-denatured protein is very difficult to avoid even by use of a surfactant. In practice, no surfactant effective for such a purpose has been found and put to practical use. Therefore, for assay of trace components in samples derived from living bodies, there is desired the development of a method which permits suppression or avoidance of measurement errors caused by insoluble materials produced by the reaction of a reagent solution with, for instance, Clq, RF or the heat-denatured protein in the sample.